The sigma (sigma) subunit of eubacterial RNA polymerase enables the holoenzyme to recognize and bind to specific sites on DNA known as promoters. Bacteria from several general possess multiple sigma factors that enable RNA polymerase to utilize difference classes of promoters. It is not known how sigma factors work to alter the specificity for promoter binding by RNA polymerase or if the sigma factors play and additional role in the initiation of transcription subsequent to binding of the polymerase to the promoter. These questions will be addresses by examining the effects of mutations in sigE, the structural gene for the sporulation-induced sigma factor, sigmaE, from Bacillus subtilis. These studies are directly relevant to understanding the regulation of differentiation and secondary metabolism in a broad range of bacteria. The understanding of the role and mechanism of sigma factor action may facilitate the production of genetically engineered strains of bacteria that produce useful products. Furthermore, the biochemical principles that govern how a protein subunit directs the bacterial RNA polymerase to specific sites on DNA are probably relevant to RNA polymerases in all organisms.